fn main() {
    int cash = 1000 // main 不是 module, 所以这里不是全局符号,而是局部变量

    // 本质是 var ave = fn():int {}
    var save = fn(int number):int {
        cash = cash + number
        return cash
    }

    print('init, cash=', cash, '\n')

    save(10)

    print('saved 10, cash=', cash, '\n')

    save(20)

    print('saved 20, cash=', cash, '\n')
}
